Recently, new system arts using the arts of processing and storing information and processing images, in combination with communication circuits, have developed rapidly. Such new system arts are referred to as the arts of visualizing electric signals which carry image information, including photographs, letters, figures and the like, on photosensitive materials through a current to a light transference (that is, the arts of obtaining hard copies from soft information).
The fields in which these system arts are utilized include acsimile, computer photo-composing system, typographic printing system, halftone image formation using a scanner, holography, and IC photomask.
The light sources installed in instruments used for these rapid transfer systems of information include a xenon flash light, a glow discharge light, an arc light, a high pressure mercury lamp, a xenon lamp, flying spots of the phosphor in a cathode ray tube, a light-emitting diode (LED), laser beams and so on. The combination of a high intensity light source as cited above and a high-speed shutter constitutes a light source apparatus.
On the other hand, the progress of silver halide photographic materials and compact simple rapid developmental systems (e.g., a minilab system) makes it feasible to provide printed photographs of extremely high quality with comparative ease at a low price. Under these circumstances, there is a strong and growing demand for obtaining hard copies from a soft information source with ease at a low price in the form of printed photographs of high quality.
The means of obtaining hard copies from a soft information source include a means which does not use any photosensitive recording material but adopts a method using electric or electromagnetic signals or an ink jet system, and a means of using a photosensitive material such as a silver halide light-sensitive material, an electrophotographic material and so on. In the latter means, a photograph record is made by the use of an optical system which emits light under the control of image information. Since the optical system itself has high resolving power and enables not only binary recording but also variable contrast recording, the latter means has the advantage that it can ensure a high quality of the images recorded. In particular, the method involving a silver halide light-sensitive material has the advantage of chemical image formation, in contrast to the method involving an electrophotographic material. On the other hand, the method involving a silver halide light-sensitive material requires particular measures to provide color sensitivities suitable for the optical system to be used, stability of photographic sensitivity, stability of latent image, high resolving power, clear separation of three primary colors, rapid and simple of color development processing, and a reasonable priced silver halide light-sensitive material.
The arts of making color copies include electrophotography-utilized copying machines and laser printers, and pictrography (trade name, products of Fuji Photo Film Co., Ltd.) in which a process comprising heat development of silver halide and diffusion of dyes, and LED are used in combination.
More specifically, JP-A-61-137149 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a color photographic material which does not undergo exposure to visible rays, and is designed so as to have on a support at least three silver halide emulsion layers into which conventional color couplers are incorporated respectively. At least two of the emulsions are sensitized to laser beams of wavelengths in the infrared region.
Further, JP-A-63-197947 and JP-A-02-157749 disclose color recording materials which have on a support at least three kinds of color coupler-containing light-sensitive layer units. At least one layer unit is spectrally sensitized so as to have its spectral sensitivity maximum at a wavelength longer than about 670 nm (that is, a sensitivity to LED and semiconductor laser beams) and to produce color images by light-scanning exposure and subsequent color development. In particular, those patent specifications disclose methods of ensuring high sensitivity and high stability to spectral sensitization and methods using dyes.
Furthermore, JP-A-55-13505 discloses a method of recording color images on a color photographic material by controlling the production of yellow, magenta and cyan colors by means of three kinds of luminous fluxes differing in wavelength, e.g., green, red and infrared fluxes.
In addition, there is a presentation of the control mechanism of semiconductor laser output for a continuous tone scanning printer and its basic features in Proceedings of "The 4th International Conference (SPSE) on Nonimpact Printing (NIP)", on pages 245 to 247, by S. H. Baek et al.
As described above, production of an apparatus utilizing laser beams (especially semiconductor laser beams) or light-emitting diodes (LED) as an exposure light source for photosensitive materials has increased in recent years. Consequently, spectral characteristics according to the wavelengths of the light emitted thereby, that is, the near infrared region, have been required of silver halide light-sensitive materials.
As for the spectral sensitizing dyes which can be used for filling such a requirement, a large number of compounds are known. Examples of such dyes include cyanine dyes, merocyanine dyes and xanthene dyes described, e.g., in T. H. James, The Theory of the Photographic Processs, 3rd Ed., pp. 198-228, Macmillan, New York (1966). They can be used alone, or in combination of two or more (e.g., for supersensitization).
Moreover, thiadicarbocyanine and selenadicarbocyanine dyes whose respective methine chains are cross-linked by a trimethylene group between the 2- and the 4-positions are known to be excellent in sensitivity, storage stability and so on, which is disclosed, e.g., in JP-A-60-202436, JP-A-60-220339, JP-A-60-225147, JP-A-61-123834, JP-A-62-87953, JP-A-63-264743, JP-A-01-155334, JP-A-01-177533, JP-A-01-198743, JP-A-01-216342 JP-A-02-42, JP-B-60-57583 (The term "JP-B" as used herein means an "examined Japanese patent publication"), U.S. Pat. 4,618,570, and so on. The dyes disclosed in those patent specifications are cross-linked by a 2,2'-dimethyltrimethylene group between the 2- and the 4-positions on the methine chain. A typical representative of such dyes is illustrated below as Dye A. ##STR2##
These dyes show their spectral sensitivity maxima in the vicinity of 700 nm, but have little or no useful function as spectral sensitizing dyes in the wavelength region longer than 730 nm.
In addition, it is reported by H. Kampfer in Proceedings of the International Congress of Photographic Science, Koln (Cologne), p. 366 (1986) that Dye A and its derivatives form J-aggregates on the surfaces of AgBrI (iodide content: 4.5 mol. %) or AgBrCl (chloride content: 20 mol%) grains to impart spectral sensitivities to such grains at wavelengths longer than 750 nm. That report, however, contains no detailed account except a brief statement that the spectral sensitivity spectra of such grains in that region were very broad.
On the other hand, other types of thiadicarbocyanine and selenadicarbocyanine dyes, in which the 2- and the 4-positions of their respective methine chains are cross-linked by a trimethylene group substituted by only one alkyl or aryl group at the 2-position, are disclosed in British Patents 595,783, 595,784, 595,785 and 604,217, U.S. Pat. Nos. 2,481,022 and 2,756,227, Photographic Science and Photochemistry, p. 39 (1987), Journal of Imaging Science, vol. 32, p. 81 (1988), and so on.
As for their ability to spectrally sensitize a silver halide system, it is reported in U.S. Pat. No. 2,481,022 that silver iodobromide sensitized by the above-cited dyes has its spectral sensitivity maximum at a wavelength ranging from 695 to 710 nm.
In Photographic Science and Photochemistry, p. 39 (1987), a silver chlorobromide emulsion (Br content: 25 mol. %, Cl content: 75 mol. %) is spectrally sensitized by the above-cited dyes to show its spectral sensitivity maximum at a wavelength ranging from 695 to 720 nm. (Amounts added per 50 g of the emulsion: 0.5 and 1 ml portions of a solution containing a dye in a concentration of 1/2000 mol/l).
In Journal of Imaging Science, vol. 32, p. 81 (1988), on the other hand, there is no description of spectral sensitivity maxima although a silver bromide emulsion is spectrally sensitized by the above-cited dyes. In that literature reference, the dyes were examined for their effect in combination with supersensitizers of the triazinostilbene type, and presumed to bring about general M-band spectral sensitization. (After the dyes were added to the emulsion in the form of a methanol solution, the resulting emulsion was allowed to stand for 20 min. at 40.degree. C.).
In general, it is difficult to achieve high sensitivity and high stability during storage in infrared sensitization, especially in sensitization at infrared wavelengths longer than 730 nm.
Also, the achievement of such characteristics is particularly difficult in the case of silver chlorobromide emulsions having a high chloride content, especially those of 95 mol. % or more. First, such emulsions suffer from lack of sensitivity, production stability and storage stability. In particular, it is hard for them to obtain a gradation which is excellent in linearity in a high sensitivity condition. Also, it is hard to get a sharp distribution of spectral sensitivities. Second, it is hard for them to obtain a high sensitivity after a short-time exposure, e.g., 10.sup.-6 -10.sup.-8 second's exposure. Third, conventional infrared-sensitizing dyes have a low adsorptivity to silver halide grains. Consequently, a lowering of sensitivity and a generation of fog tend to occur in dissolving emulsions and on standing, particularly when color couplers, a high concentration of surface active agent and organic solvents are present together. Therefore, there has been a need for the development of photosensitive materials having a high sensitivity and an excellent latent-image stability even when infrared-sensitized silver halide emulsions are used therein. Also, the development of photosensitive materials using high chloride-content silver halide emulsions which enable rapid processing has been desired in particular.